Refractory slurry and method of casting utilizing alumina coated silica solbinder and hexamethylenetetramine as a setting agent



i 6 8 ca ess REFEhr'tlGE ExAMI Ir United States Patent 0 3,507,944REFRACTORY SLURRY AND METHOD OF CAST- ING UTILIZING ALUMINA COATEDSILICA sOL BINDER AND HEXAMETHYLENETETRAMINE As A SETTING AGENT Earl P.Moore, Jr., Wilmington, Del., assignor to E. I. du 5 Pont de Nemours andCompany, Wilmington Del" a cracking may occur. A vlsual determinationWlll Indicate corporation of Delaware when the mold 15 set and then themold may be removed. NO Drawing. Filed Sept. 9, 1968, Ser. No. 758,612The resulting rt while not fi y set, has enough Int. Cl. C04b 33/02,33/12 green strength to be handled and placed in a drying oven 264-109 3Claims to further improve the green strength. Finally, the article maybe placed in a high temperature oven for firing. After the firing, thehard, shaped, completely cured article is ABSTRACT OF THE DISCLOSUREobtained.

A refractory slurry and a method of making a refractory The acidStabilized Positively charged alumina Coated article from said slurry.The slurry having a pH f l silica sol can have an ultimate particle sizeof about 4 than 5.7 consists of 50-97% refractory particles, 3-50%ngillimicrons to 0 millimicrms, P of about 3 t of a positivelygrapgumina coat iligg Ol and hex a out 6 and about 10 to 50 a solids.The preparation methylenetetr in e presen in amounts u to w nature ofthese sols are described in Alexander and Bolt, m fiie sl urry. The pHof the slurry is adjusted to US. Patent 3,007,878, Mindick and Revin,US. Patent below 5.7 prior to pouring into the mold and after pouringand Mindick and Thompson, Patent the slurry is set in the mold at anelevated temperature below 100 C. until it has sufficient strength forhandling. he he amethylenetetramine isa commercially available compound.The amount of this ingredient used is generally that amount which whentotally hydrolyzed BACKGROUND OF THE INVENTION would raise the pH of therefractory slurry to a point The preparation of refractory shapes fromthe aqueous 2 5:5 g gg: f gig f zg i g g; g g g z g g igi l'fifiiiirfrtfititi.T355333;215.1%?535; giggij jfgg j g fi fj,2Z5,.I fh,f3m;ii2 iii of 0 re ractory materia eing use e p o t e particui i tj gg?251 222 12352: fi giza g z lar refractory material will vary andnaturally less hexasecond method is to chemically set the aqueousrefractory meth-}genetetra?mefw1n be to obtam the-(issued slurry. Thecompositions presently available for this type Ea l 2 i i; ggig i addsto the Increase of chemical setting presents problems by either beingtoo Refrgctory particles such alumina silica zircon slow in settingafter the slurry is poured into the mold l f l or too fast in settingwith the resulting short pot life ml} zlrfzoma 5116a aumma grams r u mafter mixing the ingredients before pouring them into the thls InventionAdd-mommy fibers Sud-1 as Flberfrax" molds 40 "Ktalpwotzl art1dFilfaerglas are 81 5? suitagle As bknown possess the desirableproperties of a good pot life after Refracmry aggregates which whenmixed with water the initial mix of the composition and yet exhibit fastf0 1 hen the tem Nature is raised. rm an aqueous s urry to give a pH of8 or less may settmg w p be utilized In thls Invention. This would alsoInclude m1x- SUMMARY OF THE INVENTION tures of refractory particles orfibers which meet this pH An aqueou is prepared from a mixture of Posirequirement. Naturally the aggregate must be stable at tivcmmna coatedsilica sol, a minor portion an acldlc of hexamethylenetetramine and arefractory particle such T refracwry aggragines can (iontam .alkahlmpumles as, alumina, silica, mullite, Fiberfrax and Kaowool. whichmight i f out mm Solutlori to mcreaseiile When a particular refractoryparticle is selected, the pot Since h posltwely alumlnafoated 5mm 39life of the composition can be varied by the selection of the W111 begmto set at a PH f i IS ncceSarY to reamount of sol orhexamethylenetetramine as desired. Thus, dues PH caued by these lmpurmesby adding a once the refractory particle is selected the composition canmmeral The of refractory aggregates be empirically adjusted to meet theneeds of the industrial S01 f hexamethylenetetramme Shoal}! not have pHapplication being utilized. exceeding 5.7 and the pH should be ad ustedaccordingly,

preferably to a pH of about 5.4.

DESCRIPTION OF THE INVENTION The concentration of the refractorymaterial in the The components may be generally mixed i h one slurrywill depend greatly on the refractory particle size. other in any orderto form the aqueous refractory slurry. Qimerany, the refractory wouldnot be l3resent n quan The refractory particles may be added to thepositively mles greater than by Welght of the slurry of much chargedsilica sol and then thoroughly mixed with the less than 70% by welghtalthough it could go as low as sol. After thorough mixing, andhexamethylenetetramine 50% by Weight The higher refractoryConcentrations are may b add d d th mixing i ti d, best achieved withlarger refractory particle sizes. Con- During the mixing gases arefrequently ent a d i vcrsely, the lower concentrations are best achievedusing the mixture and it is desirable to remove them. In most theSmaller refractory Paftlcles $1268- part these gases would be air whichwould result in bubbles The use of Positively charged alumina CoatedSilica 501 which would weaken the final formed structure. The deandhexamethylenetetramine Preparing the aqueous gassing may be accomplishedby pressure differentials or fractofy SlulTieS of this invention give aflexible p by mechanical means such as vibrators which will essentionwhich can result in lengthened pot life (working tially dislodge the gasbubbles.

The degassed slurry is then pumped into molds of the 3,507,944 PatentedApr. 21, 1970 desired shape. The temperature around the mold isgenerally increased to 5060 C. which will result in the initial settingof the slurry. The temperature should not exceed C. since it is notdesirable at this time to drive off all of the water from the aqueousslurry because life) and yet have shorter initial setting times. Thisresults in a shaped article having a stronger green strength in shortertimes than presently available by the known processes.

Average analysis: 26% $102, 4% A1203. Average particle size: 16-17millimicrons pH 4.5 density 1.23. is prepared in a Hobart mixer. The pHof the mix is approximately 5.65. A sample of the mix has a pot life oftwo hours at 25 C.

The refractory slurry is poured into a mold. The mold is placed in a 60C. water bath. After twenty minutes of heating the ceramic slurry isset, the mold is removed, and the ceramic form can be handled.

EXAMPLE 2 Five pounds of the refractory slurry of Example 1 is prepared.The amount of hexamethylenetetramine is increased to one-tenth of onepercent. The pH of the mix is approximately 5.65. A sample of the mixhas a pot life of two hours at 25 C.

The refractory slurry is poured into a mold. The mold -is placed in a 60C. water bath. After twelve minutes of heating the ceramic slurry isset, the mold is removed and the ceramic form can be handled.

EXAMPLE 3 Five pounds of the refractory slurry of Example 1 is prepared.The refractory slurry is poured into a mold. The mold is placed in a 90C. water bath. After nine minutes of heating the ceramic slurry is set,the mold is removed and the ceramic form can be handled.

EXAMPLE 4 Five pounds of a refractory slurry consisting of:

Percent -325 alumina 35.0 -28+100 alumina 9.5 14+28 alumina 15.3 8+14alumina 29.0 Binder of Example 1 9.0 Water 2.0 Hexamethylenetetramine .1

is prepared in a Hobart mixer. The pH of the mix is approximately 5.7. Asample of the mix has a pot life of one and a half hours at 25 C.

The refractory slurry is poured into a mold. The mold is placed in a 60C. water bath. After twenty minutes of heating the ceramic slurry isset, the mold is removed, and the ceramic form can be handled.

EXAMPLE 5 Five pounds of a refractory slurry consisting of:

Percent 325 alumina 23.6 -325 fused silica 15.7 200+325 fused silica23.6 -40+60 fused silica 15.7 Binder of Example 1 20.5 Water .4Hexamethylenetetramine .3

is prepared in a Hobart mixer. The pH of the mix is approximately 5.5. Asample of the mix has a pot life of greater than eight hours at 25 C.

The refractory slurry is poured into a mold. The mold is placed in a 90C. water bath. After seven minutes of heating the ceramic slurry is set,the mold is removed, and the ceramic form can be handled.

EXAMPLE 6 Five pounds of a refractory slurry consisting of:

Percent 325 zircon 63.4 10 100+200 zircon 15.3 Binder of Example 1 21.0Hexamethylenetetramine .3

is prepared in a Hobart mixer. The pH of the mix is approximately 5.3. Asample of the mix has a pot life of greater than twenty four hours at 25C.

The refractory slurry is poured into a mold. The mold is placed in a 90C. water bath. After twenty minutes of heating the ceramic slurry isset, the mold is removed, and the ceramic form can be handled.

EXAMPLE 7 Five pounds of a refractory slurry consisting of:

Percent 325 mullite 67.1 -65+100 mullite 7.5 Binder of Example 1 25.0Hexamethylenetetramine .4

is prepared in a Hobart mixer. The pH of the mix is approximately 5.5.-A sample of the mix has a pot life of greater than seven hours at 25 C.

The refractory slurry is poured into a mold. The mold is placed in a 90C. water bath. After twenty eight minutes of heating the ceramic slurryis set, the mold is removed, and the ceramic form is able to be handled.

EXAMPLE 8 Five pounds of a refractory slurry consisting of:

Percent -325 fused silica 38.0 -200+325 fused silica 22.8 -8+50 fusedsilica 15.3 Binder of Example 1 23.5

Hexamethylenetetramine .2

is prepared in a Hobart mixer. The pH of the mix is approximately 5.2. Asample of the mix has a pot life of greater than twenty four hours at 25C.

The refractory slurry is poured into a mold. The mold is placed in a 90C. water bath. After one and a half hours of heating the ceramic slurryis set, the mold is removed, and the ceramic form is able to be handled.

\What is claimed is:

1. Alwl illi rgyfor preparing refractory articles which has a p o essthan 5.7 consisting essentially of 50-97% by weight of the slurry of arefractory material selected from the groupconsisting of alumina fusedsilica, mulmQJimfQ and mixtures thereof, 3 5%% by weight of the slurryof a binder of,positively charged wted s il i ca sol having an ultimateparticle size of about 4-100 millimicrons and a pH of about 3-6, and

hexamethylenetetramine present in an amount up to 1% by weight of theslurry.

2. A slurry as in claim 1 where said refractory is present in an amountof about 70% to 97% by weight based on the slurry weight.

3. In a process for preparing shaped refractory articles from refractorymaterials selected from the group consisting of alumina, fused silica,mullite, zicron, and mixtures thereof, by mixing the material with aninorganic binder in an aqueous slurry, setting the mixture in a mold.removing the mold and firing the molded article, the improvementcomprising using 3-50% by weight of the slurry of a positively chargedalumina coated silica sol having an ultimate particle size of 4-100millimicrons and a pH of about 3-6 as the binder along withhexarnethylenetetramine in an amount up to 1% by weight of the slurry,where the pH of said slurry prior to molding is adjusted to less than5.7, and setting the mixture at an elevated temperature no greater than100 C.

References Cited UNITED STATES PATENTS 6 3,252,917 5/1966 Mindick et al.252-313 3,312,631 4/1967 Smith 264-l5 3,445,250 5/ 1969 Preece 106-65FOREIGN PATENTS 764,000 7/ 1967 Canada. 967,934 8/1964 Great Britain.

DONALD I ARNOLD, Primary Examiner 10 I. H. MILLER, Assistant ExaminerUS. Cl. X.R.

